Method of producing a spray bonded multi-ply tissue product

ABSTRACT

Multi-ply tissue product is bonded by an adhesive spray whose position is controlled so that the web path distance between the spray application and the location where the webs are forced together permits sprayed adhesive to partially but not completely set during travel over that web path distance at operating web speeds. Typically, the web path distance between the nozzle and the location is more than 140 inches. The webs are positioned one in back of the other and each is unwound onto its own carrier roll, with the spray positioned between the carrier rolls.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional application of and claims priority toU.S. application Ser. No. 08/628,386, filed on Apr. 5, 1996, now U.S.Pat. No. 6,136,422, which is hereby incorporated by reference.

TECHNICAL FIELD

This invention is in the general field of multi-ply tissue products aswell as methods and apparatus for bonding tissue plies to make suchproducts.

BACKGROUND

Various tissue products are made by laminating multiple layers oftissue. These layers or plies must be bonded to prevent them fromdelaminating or floating apart when they are converted into the finalproduct or when they are used by the consumer.

Ply bonding of the individual tissue sheets into multi-ply layers isusually achieved by embossing them on converting equipment withoutapplying adhesive. In this process, two or more tissue webs aresimultaneously unwound and fed through a nip formed between male andfemale embossing rolls to emboss or crimp the webs and thereby bond themtogether. Often in making such products as napkins, the webs areembossed only around the perimeter of areas that will be cut into theindividual napkins.

In a different process, tissue plies may be adhered using a chemicaladhesive rather than by embossing. For example, Björk U.S. Pat. No.5,466,318 discloses a process for laminating webs using a water-basedadhesive.

Controlling ply bonding is important and difficult. Inadequate,excessive or inconsistent ply bonding can jam complex, high-speedmachinery, generate high waste, and provide unacceptable product. Thestrength of bonding by embossing (without adhesive) may vary depending,among other things, on water content or dryness of tissue webs, and onambient air humidity. While bonding by embossing sometimes can beimproved by increasing the pressure on the embossing rolls, suchpressure can wear out the embossing rolls more quickly, particularly thefemale roll, which is usually a softer roll made of composite materialonto which a pattern is impressed by the opposing, male, engraved metalroll. In addition, the journals and bearings of both embossing rolls canalso wear out prematurely if subjected to increased pressure over aprolonged period.

The use of adhesives can avoid some of the problems of embossing, butadhesives also cause problems, such as “through bonding” or “blocking”,in which adjacent laminates bond to one another, and, prevent unwindingof the laminate product from its roll. Non-uniformity of bonding alsocauses problems, such as wrinkling of the tissue and bad printing.

As noted, the bonding process may be part of the overall process formaking the final multi-ply product. For example, multi-ply tissueproducts, particularly napkins, may be printed, e.g., by a letterpressor a flexographic process. In a typical letterpress printing process, amulti-ply web is first embossed, and then the central unembossed area ofindividual napkins is printed. In an alternative flexographic printingprocess, unbonded webs may be first run through a flexographic printingtower and then crimped with an embossing nip.

While the invention has broader application, we refer specifically tocertain markets, particularly high quality napkins such as the partygoods, food service, and other specialty napkin markets. These marketsmay require cloth-like character and feel, high wet strength, and theability to be decorated with high quality printing. Increasingly, thesemarkets have expressed preference for quality and complexity provided byflexographic printing.

It can be difficult to achieve cloth-like character and feel while alsoachieving satisfactory bonding of two or more plies of tissue to makeone sheet of napkin tissue that will not come apart either when used bythe consumer or when subjected to flexographic printing. The napkin mustnot de-ply, it must stay in one piece like a cloth napkin would.However, the use of adhesives and other additives to develop theresistance to ply separation tends to make the product stiff and destroythe cloth-like feel.

Another product requirement in this field is the need of strength whilewet, which can be critically important to high quality paper napkins.Non-wet strength napkins may pull apart when subjected to moisture, suchas spilled liquid or a wet glass, rendering then unsatisfactory for thehigh quality markets. Chemicals normally employed to impart wet strength(e.g., urea, phenol-formaldehyde) can reduce ply bond-strength, which isalready problematic, and can make the napkin stiffer.

With regard to decorated or printed napkins, certain napkin machines(e.g., those made by Servotec and Hoberna), which use flexographicprinting have stringent ply requirements. As noted, these flexographicmachines print the napkin first and emboss it afterwards, in contrastwith letterpress napkin machines, which first emboss the edges of thenapkin so that the plies of tissue are crimped together, after which thenapkin is printed. In the flexographic process, it is critical that theplies be held together without embossing while the napkin is beingprinted. Floating plies as the tissue enters the printing stage resultin jams and high waste together with machine downtime. In addition, theapplication of the ink causes the top layer of the tissue to expand ifthe plies are not well bonded, resulting in wrinkling, badly printednapkins, and extremely high costs from waste.

These problems are sometimes addressed by the use of much heavier napkintissue (as has been done in Europe where some of the flexographicmachines were introduced). Heavier tissue is more expensive.

SUMMARY

We have discovered spray bonding processes and apparatus that providesubstantially improved efficiency and process control of tissue bonding.The resulting adhesively bonded intermediate product is improved,particularly for use in flexographic printing applications. The finalproduct may be a paper napkin, a paper towel, a medical disposabletowel, a table cover or other similar tissue product. The cloth-likefeel achieved by the invention is suitable for a wide range of markets,including not only markets where softness is important but also marketswhere a certain amount of product stiffness is required, such as themarkets in which napkins are forced into plastic wraps containingcutlery (napkins made and packaged by “Austin-Gordon” or “Gordon”-typemachines)

In particular, the invention provides a well-bonded napkin product thatcan be used in converting apparatus, particularly flexographic printingapparatus. This ply-bonded tissue is constructed of lighter weightmaterial that is less costly than the previously used tissue(particularly in Europe), yet the tissue exhibits printability and acloth-like feel. Cloth-like character and feel, high wet strength,printability and low cost are achieved in a reliably ply-bonded productwithout the need to emboss before printing. The result is markedlyenhanced ply bonding of the tissue layers and efficient and high qualityprinting, without detracting from the cloth-like character and feel thatthe use of adhesives can cause.

One aspect of the invention generally features a multi-ply adhesivelybonded tissue roll with an extremely limited amount of waste at thecore, which results from the absence of bonding or poorly controlledbonding during start-up of the bonding process. The roll comprises abonded region that extends to within at least ¾ inch of the core. (This¾ inch measurement is made from the outer diameter of the core, which istypically about 4 inches to the point in the product at which adhesivebonding begins.) Adhesive contact between the plies is substantiallycontinuous over the bonded region of the roll (i.e., at radiuses greaterthan ¾″), and the strength throughout the bonded region of the roll ishigh, substantially without through bonding in that region. While bondstrengths of at least 100 mg/cm are achieved, in one particularembodiment, the bond strength is at least 400 mg/cm.

In another aspect of the invention described below, we have found thatcareful process control permits lower adhesive loading and the use of apressurized nip to force the webs together without unacceptable adhesivebuild-up on the nip rolls, particularly for two-ply tissue product.Strong two-ply adhesion can be achieved with lower adhesive loading,thus avoiding problems caused by inconsistent adhesive loading while atthe same time enabling better control over winding tension (because thenip controls tension transmitted upstream). Thus, this aspect of theinvention features methods of producing an adhesively bonded two-plytissue product by: spraying an adhesive mixture upwardly onto one of themoving webs from at least one nozzle array positioned in a spraylocation below one of the webs; compressing the webs together as theyrun through a nip formed by two nip rolls positioned at a compressionpoint downstream of the spray location; and winding the bonded two-plytissue product onto a roll under tension using a winder which pulls thetwo-ply product, exerting tension on it. In this aspect of theinvention, it is practical to use a pressurized nip to force theadhesively bonded webs together. The distance between the spray locationand the nip is selected to permit sprayed adhesive to partially but notcompletely set during travel over that distance at operating web speeds.The webs may be forced together with nip rollers that have enoughpressure to substantially confine winder tension to the nip-to-winderportion of the web path, as opposed to transmitting winder tensionupstream to the parent reels (i.e. the reels on which the tissue stockhas been supplied to the bonder), thereby providing improved controlover winder tension. Because the spray location is carefully controlled,it is possible to use such a nip without unacceptable adhesive build-upon the nip rolls.

In the above process, the adhesive is considered to be partially but notcompletely set when it has what is known in the field as “green tack”.At that stage, the adhesive is damp to the touch, but it does nottransfer to another surface, so the adhesive will contact bond, but itwill not migrate so far through the tissue web that it causes throughbonding as the bonded webs are wound into a roll.

Typically, each tissue web is unwound over its own carrier roll, andspray nozzle(s) are positioned between the carrier rolls, particularlyadjacent to and downstream of the rear carrier roll. For example, theweb travel distance between the nozzles and the nip is more than 140(and even more than 200 but less than 500) inches.

In a third aspect, the invention features methods of producing tissueproduct with more than 2 (usually 3 or 4) plies. The method uses atleast two spray nozzle arrays, a rear array to spray the bottom of anupper web and a forward array to spray the bottom of an intermediateweb. The multiple webs are tensioned by a winder around a compressionroll (usually but not necessarily a nip roll as described above) tocompress the webs. The web travel distance between the two nozzle arraysand the nip roll is controlled so that adhesive is partially but notcompletely set when it reaches the roll. Both nozzle arrays arepositioned as discussed above. Typically the forward nozzle array willbe more than 140 inches (preferably more than 200 inches) from thecompression roll.

Preferably, webs are run at a speed of well over 1500 feet/min (more mepreferably 2,300 feet/min or higher), and the dwell time for adhesiveapplied to the web is between 0.3 and 1.3 seconds. Dwell time is theperiod from application of adhesive to the web until the adhesivetreated web reaches the nip.

Alternatively, to make three- or more ply product, the number of sprayerlocations may be two less than the number of plies being bound. Forexample, four moving webs are positioned vertically to form an upperweb, a upper-middle web, a lower-middle web, and a bottom webrespectively, and only two arrays of adhesive spray nozzles are used: afirst array positioned in the rear location to spray upwardly onto thebottom surface of the upper-middle web; and a second array positioned ina third location to spray upwardly onto the bottom of the lower-middleweb. Similarly, the method may be used to make three-ply tissue bypositioning three moving webs as an upper web, a middle web, and a lowerweb, respectively, and using only one adhesive nozzle array, which ispositioned in the rear location to spray upwardly onto the middle web.

A significant advantage of the method is that it can be used in serieswith high-speed tissue-forming equipment, i.e., reels of tissue webs areprovided by forming them on equipment including a dryer, and winding upthe resulting webs, which then are bonded at a rate which exceeds therate at which the webs are produced. When we say that the webs arebonded at a rate which exceeds the rate at which the webs are produced,we take into account down time at the beginning of a run for loadingreels of freshly made unbonded tissue and time at the end of a run tounload bonded multi-ply tissue. We also take into account similar downtime for the tissue production process. Finally, we take into accountthat at least two and sometimes three or four tissue webs must be madeto produce a single multi-ply bonded web so that, as a roughapproximation and if all other things were equal, a two-ply bondingprocess could run at ½ the speed of the tissue manufacturing processwithout becoming a bottleneck. In general, the web speed exceeds 1500feet/min (preferably over 2000 feet/min) during a significant portion ofthe bonding process.

Tissue making relies on management of the creping process, in whichdried tissue is scraped from a heated drying cylinder to which it hasbeen adhered. Creping is improved generally when the drying cylinder ishot and the tissue is relatively dry at the point of creping. The abovedescribed bonding process is advantageous in that it can bond relativelydry webs, without adding or retaining moisture at the tissue-formingstage to accommodate the needs of the bonding process.

Control over the spray process may include controlling the adhesivemixture flow with respect to web travel speed, for example, to maintaina substantially constant (+or −20%) overall rate of addition of dryadhesive per unit area of web at different speeds (preferably theaddition rate is between 5 and 25 (most preferably between 5 and 20)pounds/million square feet of multi-ply web). The method may alsoinclude controlling the air pressure used to spray the mixture atdifferent web travel speeds.

Typically, the method includes at least two phases, a running phase anda substantially slower transition phase (e.g., starting up or slowingdown the winder). The amount of liquid adhesive delivered per minute issubstantially proportional (±20%) to the web speed during both therunning phase and the transitional phase. The atomizing airflow pressureor flow rate may also be controlled responsive to changes in web travelrate between the running and the transition phase.

Multiple nozzles may be positioned on supports in a shower housing whichincludes a drain for over-spray. The shower housing includes a damperthat is movable from a first damper orientation that prevents nozzlespray from reaching the moving web to a second damper orientation inwhich spray reaches moving web. During the start-up phase, the damper ispositioned in the first orientation so that web is not bonded. Theshower housing may be raised from a an inactive position during idleperiods when the web is slowed or stopped to a second active position.Adhesive may be purged from the nozzles in a cycle that includesintroducing flush water and/or airflow into the shower nozzle.

Preferred adhesives are aqueous mixtures, e.g., of carboxymethylcellulose; polyvinyl alcohol; or starch. The spraying process controldescribed above enables the use of higher (for example at least 13%)solids in the liquid adhesive, which in turn results in shorter dryingtimes.

After the adhesive is applied, the webs may be forced together by a pairof rolls (e.g. calender rolls) that are in contact as the two webs passthrough. For example, these rolls may be biased together to form apressure nip. The bonded tissue plies are then wound up on a winderdownstream of the nip, and tension on the winder is substantiallymaintained downstream of the nip and is not substantially communicatedupstream of the nip.

II. Apparatus

The above method is practiced using apparatus that includes:

A. a rear reel stand and a rear carrier roll above the rear stand,forming the beginning of an upper web path;

B. a forward reel stand and a forward carrier roll above the forwardstand, forming the beginning of a lower web path, the upper web pathconverging with the lower web path at the forward carrier roll;

C. an adhesive applicator system for applying adhesive to the bottom oftissue moving in the upper web path, the adhesive applicator systemcomprising:

i. an array of spray nozzles positioned at a spray location below andgenerally transverse to the upper tissue path, and oriented to spraygenerally upward, toward the bottom surface of the upper tissue, thefirst location being between the rear and the forward carrier rolls;

ii. an air pressure source connected to provide air to the spray nozzles

iii. an adhesive source connected to provide a flow of adhesive to thespray nozzles, and

D. a pair of nip rolls positioned downstream from the spray head arrayand the forward carrier roll, the nip rolls being in both the upper andlower tissue paths, the nip rolls forming a nip for compressing theupper and the lower tissue together

E. a winder downstream of the nip for winding up bonded tissue product,the winder being designed to have a running speed within a predeterminedrange,

the nip being spaced apart from the spray location at least 230 inches,to permit sprayed adhesive to partially but not completely set duringtravel over that distance at speeds in the predetermined range.

The location of the array of spray heads is controlled as describedabove. For example, the nip is spaced apart from the first (rear)location by at least 200 inches to permit sprayed adhesive to partiallybut not completely set during travel over that distance. Specifically,the array is located between the rear and the forward carrier rolls.

The apparatus may also include: A. an adhesive pump providing a flow ofadhesive to the spray heads; B. an air pump providing air pressure tothe spray heads; C. a sensor for sensing the speed of travel of at leastone of the tissue webs, which provides a web speed signal to a signalprocessor; and D. an adhesive flow control system for controlling theflow of adhesive to the spray heads; the adhesive flow control systemincludes a flow rate monitor, a signal processor which receives a signalfrom the monitor and provides signals to an adhesive flow motor,responsive to the web speed signal, so that the adhesive delivery rateis varied in response to web travel rate.

When more than two tissue webs are being bound, the apparatus includesat least one intermediate reel stand and intermediate carrier roll,forming the beginning of an intermediate web path, the intermediatecarrier roll being positioned between the rear and the forward carrierrolls. The apparatus may also include additional arrays of spray headspositioned at a second (forward) location below and generally transverseto the intermediate web path, and oriented to spray generally upward,toward the bottom surface of the intermediate tissue.

The apparatus can operate fast enough to process the output of theweb-forming equipment substantially without backlog or slowing of thatequipment.

A signal processor includes circuitry to control the amount of adhesiveflow supplied to the nozzles substantially proportional to the webtravel speed, so as to provide a substantially constant overall ratio ofdry adhesive per unit area of web at different web speeds. Thecontroller also includes circuitry to establish the other methodcontrols described above, such as the controls on adhesive flow, airflowdamper position, and shower housing position. The controller alsocontrols a purge cycle in which flush water and/or airflow is directedinto the nozzle.

As noted, the above process and apparatus use tissue that is very drywithout need for further modification. The process avoids the need toemboss as a bonding process. The process permits effective use of highspeed tissue forming machinery. The process improves utilization andreduces waste, particularly waste from discarding the beginning and endof rolls due to improper adhesive loading at transition speeds.

The details of one or more embodiments of the invention are set forth inthe accompanying drawings and the description below. Other features,objects, and advantages of the invention will be apparent from thedescription and drawings, and from the claims.

DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram showing apparatus for spray bonding two movingtissue webs.

FIG. 2 is a chart of a operating sequences during a process for spraybonding moving tissue webs.

FIGS. 3A through 3C are top, front and side views, respectively, of ashower housing.

FIG. 4 is a diagram of the valves and supply conduits for the housing ofFIGS. 3A-3C.

FIG. 5 is a sectional view of a nozzle.

FIG. 6 is a diagram of controls for the apparatus of FIG. 1.

FIG. 7 shows an alternative embodiment for producing four-ply tissue.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

In FIG. 1, individual tissue webs 10 and 20 are spray bonded on plybonder 40 to form a two-ply tissue product 30. Bonder 40 includes tworeel stands 42 and 44 suitable to receive webs as they are produced bytissue forming apparatus (not shown).

Webs 10 and 20 are unwound from the reel stands and threaded overcarrier rolls 46 and 48 to roll 49 and from there to calender rolls 50and 52 and winder 54.

A shower assembly 60 is positioned between carrier rolls 46 and 48,beneath, and across the width of (i.e. transverse to the movement of),web 10. Shower assembly 60 (shown in greater detail in FIGS. 3A-3C)includes a row of nozzles (shown in FIG. 4) positioned in a rectangularhousing 64, which extends across the width of the web (about 112 inches)and the housing section (FIG. 3C) is about 9×11 inches. Housing 64(shown for clarity in FIGS. 3A-3C without nozzles) includes severalfeatures described in greater detail below. Axle 66 extends across thewidth of the housing, and it controls rotation of a baffle plate (or“flapper”) 68. A trailing lip 70 extends from the rear (trailing) edgeof housing 64. Side ports 72 are provided for air adhesive conduits(shown in FIG. 4) which supply nozzles 62.

FIG. 4 shows an array of 12 nozzles 62 spaced about 8.75 inchescenter-to-center. Generally, the number of nozzles is selected toprovide 200% coverage—i.e., any given point on the web generallyreceives output from two nozzles. As described in greater detail below,each nozzle is connected to a liquid adhesive supply 63, and atomizingair supply 65 and a control air supply 67.

A representative nozzle 62 is shown in FIG. 5. The nozzle comprises acontrol chamber 74 which drives a shut-off and clean-out pin 76 to shutoff or open orifice 78. Adhesive is supplied from one side port 80, andair is supplied from an atomizing air port 82 on the other side of thenozzle. The pressure in chamber 74 overcomes the spring bias, drivingpin 76 rearwardly and opening orifice 78. Generally, the nozzle producesa fine flat fan spray with a fairly wide spray angle (thus reducing thenumber of nozzles needed). The wider the spray angle, the fewer nozzlesthat are required, thus reducing costs and generally stabilizing andmaximizing adhesive flow in any single nozzle.

FIG. 6 is a diagrammatic representation of the systems that supply andcontrol the equipment described above.

Shower assembly 60 and supply conduit 63 are connected to adhesivereservoir 102 and supply pump 103 via supply conduit 104, which includesfilter 105 and valve 120. Pump 103 is a positive displacement pump,driven by a variable speed motor to control adhesive flow. A magneticflow meter 107 monitors flow in conduit 104. Valves 120 and 121 as apair can be set to direct adhesive flow to conduit 63 (valve 120 openand 121 shut) or to return loop 123 which returns adhesive to supply 102when valve 121 is open and 120 is shut.

The shower assembly is connected to atomizing air supply conduit 65(introduced through both sides of housing 60) from air supply 106.Atomizing airflow is controlled by supply valve 109.

Nozzle control air is provided via conduit 67, and is controlled bypneumatic valve 134, which is supplied by air supply 106.

Flapper control arm 69 is connected to pneumatic controller 71, which issupplied from via air supply conduit 106. Flush water supply 91 isconnected to atomizing air supply conduit 65 via control valve 115 andcheck valve 117. Shower housing assembly lift mechanism 108 iscontrolled by pneumatic valve 131 which is pressurized by air supply 106via conduit 133.

Quick purge valve 140 opens the atomizing air conduit 65 to purge anyliquid in it at the end of the purge cycle described below.

A computer (signal processor) 100 is separately connected to adhesivesupply pump 103 and to air supply valve 109. Computer 100 is alsoconnected to control the speed of pump 103 responsive to signals itreceives from: a) flow meter 107; b) operator input of the adhesive flowset point; and c) winder speed. Computer 100 is also connected to othercomponents as described above and shown in the figures.

A system of compressed air supply 106 supports the number of operationsdescribed above, e.g., it provides pressure and volume to operate thespray nozzles and various system components described below. Thecompressed air capacity required will vary depending on the needs of aparticular system. Generally, a source on the order of 40CFM at 80 psiis adequate.

Computer 100 reads the winder speed (WS), the adhesive flow (AF) and anycontrol modes supplied by operator input 113. From these values,computer 100 calculates the required adhesive flow (AF), so thatAF=K×WS×SP, where WS is the winder speed; SP is an operator supplied setpoint for the adhesive loading—i.e., dry weight of adhesive per area ofweb. The set point for making a two-ply product typically will be on theorder of 5-25 (more preferably 5-20) pounds of dry adhesive per millionsquare feet of web. When three-ply tissue is made with two showers, eachshower is set in the above range. Where a single shower is used to bondthree plies, the adhesive spray must penetrate the middle layer to bondboth the upper and lower layer. In that event, the set point for thatshower is higher (e.g. in the range of 30-35 pounds/million squarefeet). “K” is a proportionality constant that takes into account thewidth of the winder, the density of adhesive mixture (gallons of mixtureper unit of dry adhesive weight) and that reconciles and scales unitsused.

Computer 100 also is programmed with routines to

1. start, stop and control the speed of the adhesive feed pumps;

2. start, stop and regulate atomizing air;

3. turn control air on and off;

4. open and close the flapper;

5. raise and lower the shower box;

6. toggle adhesive diverting valves;

7. flush the shower by,

i. starting and stopping flush water,

ii. opening and closing the quick purge valve,

iii. starting and stopping the atomizing air;

The operation of the above-described equipment will be better understoodwith reference to the following operating sequences diagrammed in FIG.2. Overall operation can be divided into a start-up cycle, a normalrunning mode, and a shutdown cycle. The operator may select manual orautomatic operation. At rest (col. 1), the winder is off, a runinterlock is open, the adhesive flow is off, the atomizing air is off,the shower housing is in the lower, inactive position, the flapper isclosed, the control air is off, valves in the adhesive flow loop are setto recycle adhesive to the supply (i.e., valve 120 is closed and valve121 is open), flush water is closed, and purge air is closed.

In automatic operation, the computer begins start up with a threadingmode (col. 2) by turning the winder on to a slow, threading speed, andturning on the pump to begin adhesive flow (with valve 121 remainingopen and valve 120 remaining closed). The computer then enters a mode inwhich the web is running (col. 3) by closing the run interlock, turningon the atomizing air valve 107, and moving the shower housing and theflapper into operating positions. Once the web running status isachieved, there are two two-second speed-up checks (cols. 4 and 5) asthe winder speed is increased. Control air is turned on between thesetwo checks.

Immediately after the second speed check, diverter valve 121 is closedand supply valve 120 is opened to start adhesive flow to the nozzles.The apparatus is then in its normal running mode (col. 6).

Shut-down includes several phases, and it may be initiated manually orautomatically as the winder slows and a low speed threshold (e.g. <100feet/min) is reached.

In shut down, atomizing air is ramped down with the winder, and thenboth are turned off. The run interlock is opened, and adhesive flow isdiverted by closing valve 120 and opening valve 121. The shower housingis lowered and the flapper is closed. Nozzle control air pressure isalso shut off.

A nozzle wash cycle is achieved by introducing flush water into theatomizing air conduit 65. A nozzle air purge cycle (col. 9) is achievedby turning off flush water, and starting atomizing air flowing throughthe nozzles. Atomizing airflow is increased for the final purge (col.10) by opening quick purge valve 140 at the far end of the nozzlehousing. When the atomizing air and quick purge valve 140 are turnedoff, the system is at rest (col. 12).

A flush mode as described above can be instituted manually whenever theshower is in auto mode and the winder is not running. The water valvewill stay open for as long as 15 minutes (compared to the 15 seconds inthe auto mode).

A manual mode permits each of the control functions to be operatedmanually and independently.

Bond strength of the product may be tested according to a standardizedprotocol. For example, small strips of bonded product (typically about2.5 inches wide) are subjected to known force to determine the amount offorce required to separate the tissue layers. In general, forflexographic product applications, the bond strength should exceed 100mg/cm. Preferably the median value of the bond strength should be over400 mg/cm. If necessary, the measured force for separating a given stripmay be doubled using two strips, and obtaining a value for separatingboth strips.

Because the product is bonded with a carefully controlled adhesivespray, the adhesive is substantially continuous and uniform, even whenanalyzed at a detailed level. For example, when a starch or PVA adhesiveapplied by the above spray is evaluated using a standard iodinevisualizing procedure (e.g., spraying a 0.01N I₂ solution on the tissuefrom a standard pump sprayer), color development indicative of adhesiveshows very little non-uniformity, and what non-uniformity exists isgenerally random, at least over areas greater than 1 mm². In contrast,adhesive applied by a textured roll will show a regular uniform matrixof starch dots over areas up to 1 cm².

Other embodiments are within the following claims. For example, in FIG.7, each of four reel stands 301-304 is occupied, and one of carrierrolls 305-308 is included to carry web from each of the respectiverolls.

Only two shower assemblies 309 and 310 are positioned between carrierrolls 301 and 302, and between 302 and 303, respectively. No shower isnecessary or desirable between carrier rolls 303 and 304. Instead, theadhesive load from shower 309 is increased to provide sufficientadhesive to bond webs 303 and 304.

In an alternative embodiment (not shown) three-ply tissue may bemanufactured by omitting the roll on stand 301. Shower assembly 310 isoptional in that configuration. A number of embodiments of the inventionhave been described. Nevertheless, it will be understood that variousmodifications may be made without departing from the spirit and scope ofthe invention. Accordingly, other embodiments are within the scope ofthe following claims.

What is claimed is:
 1. A method of producing an adhesively bondedmulti-ply tissue product by: A. providing at least two reels of tissue;B. unrolling each of the reels to produce at least two moving webs, theweb speed being over 1500 feet/min; C. spraying an adhesive mixtureupwardly onto at least one of the moving webs from at least one nozzlearray positioned in a spray location below one of the webs; D.compressing the webs together as they run through a nip formed by twonip rolls positioned at a compression point downstream of the spraylocation; and E. winding the bonded multi-ply tissue product onto a rollunder tension using a winder which pulls the multi-ply product, exertingtension on it, the method being further characterized in that the niprolls are forced together by a force sufficient to isolate the tensionto a region between the nip and the winder.
 2. A method of producing anadhesively bonded multiply tissue product by: A. providing at least tworeels of tissue; B. unrolling each of the reels to produce multiplemoving webs, the web speed being over 1500 feet/min; C. spraying anadhesive mixture upwardly onto at least one of the moving webs from atleast one nozzle array positioned in a spray location below at least oneof the webs; D. winding the bonded multi-ply tissue product onto a rollunder tension using a winder which pulls the multi-ply product, exertingtension on it, the method being further characterized in that the amountof adhesive flow provided to the spray head is directly controlled withrespect to, and a function of, the web travel speed, so as to provide acontrolled overall ratio of dry adhesive per unit area of web atdifferent web speeds.
 3. A method of producing an adhesively bondedmulti-ply tissue product having at least three plies by: A. providing atleast three reels of tissue; B. unrolling each of the reels to produceat least an upper moving web, a middle moving web and a lower movingweb, the web speed being over 1500 feet/min; C. spraying an adhesivemixture upwardly onto the upper moving web from a rear nozzle arraypositioned in a rear spray location below the upper moving web; D.spraying an adhesive mixture upwardly onto the middle moving web from aforward nozzle array positioned in a front spray location below themiddle moving web; E. compressing the webs into the bonded multi-plytissue product by winding the webs together under tension from a winderaround a roll positioned downstream of both the rear spray location andthe front spray location to force the three webs together; the methodbeing further characterized in that, F. both the front and the rearspray locations are spaced from the roll at web path distances selectedto permit sprayed adhesive to partially but not completely set duringtravel over that distance at operating web speeds, whereby the adhesivemixture bonds the webs together into the adhered multi-ply product. 4.The method of claim 3 in which step E. comprises feeding three websthrough a nip formed by two nip rolls which are forced together by aforce sufficient to isolate winder tension to the web region between thenip and the winder.
 5. The method of claim 1, claim 2 or claim 4 inwhich the spray and compression locations are spaced apart a web pathdistance between the nozzle array and the nip is more than 140 inches.6. The method of claim 5 in which the web path distance between thenozzle array and the nip is more than 200 inches.
 7. The method of claim1, claim 2, or claim 4 in which the web path distance between the nozzlearray and the nip is less than 500 inches.
 8. The method of claim 1,claim 2, or claim 3 in which the webs are run at a speed of over 2300feet/min.
 9. The method of claim 1 in which web speed results in a dwelltime for adhesive applied to the web between 0.3 and 1.3 seconds, saiddwell time being the time for a point on the webs to travel from saidspray location to said compression point.
 10. The method of claim 1 orclaim 2 in which the tissue product is a two-ply product.
 11. The methodof claim 1, claim 2 or claim 3 in which the tissue product is athree-ply product.
 12. The method of claim 1, claim 2 or claim 3 inwhich the tissue product is a four-ply product.
 13. The method of claim1, claim 2, or claim 3 in which the number of plies=n, and the number ofshowers=n−1 or fewer.
 14. The method of claim 1, claim 2, or claim 3 inwhich: the tissue webs are provided by forming them on web-formingequipment including a dryer, and rolling up the resulting webs toproduce the tissue reels, and the webs travel at a rate fast enough toprocess output of the web-forming equipment substantially withoutbacklog or slowing of the web-forming equipment.
 15. The method of claim14 in which the webs are produced by in a process that includes dryingthe webs, and, after said drying, the webs contain no more than 6.5%water; and then creping the dried web.
 16. The method of claim 1, claim2 or claim 3 in which the adhesive is an aqueous mixture.
 17. The methodof claim 16 in which the adhesive is an aqueous mixture of carboxymethylcellulose; polyvinyl alcohol; or starch.
 18. The method of claim 1,claim 2 or claim 3 further comprising converting the tissue product intoa final product.
 19. The method of claim 18 in which the final productis a paper napkin, a paper towel, a medical disposable towel, or a tablecover.
 20. The method of claim 1, claim 2 or claim 3 in which the amountof adhesive flow provided to the spray head are controlled with respectto the web travel speed.
 21. The method of claim 20 in which the amountof adhesive flow supplied to the nozzles is substantially proportionalto the web travel speed, so as to provide a substantially constantoverall ratio of dry adhesive per unit area of web at different webspeeds.
 22. The method of claim 21 comprising at least two phases, arunning phase and a transition phase, the web speed during at least partof the transition phase being substantially slower than the runningphase, and the amount of liquid adhesive delivered per minute beingsubstantially proportional to the web speed during both the runningphase and the transitional phase.
 23. The method of claim 22 in whichthe transition phase follows a start-up phase after the equipment hasbeen idle.
 24. The method of claim 23 in which the adhesive additionrate is maintained at between 5 and 20 dry pounds per million squarefeet of web during the running phase and the transition phase.
 25. Themethod of claim 23 in which the transition phase accomplishes slow downfrom running.
 26. The method of claim 25 in which the pressure or flowof nozzle atomizing air is controlled in response to web speed changeduring the transition phase.
 27. The method of claim 1, claim 2, orclaim 3 in which each of the nozzle arrays is positioned in a showerhousing which includes a damper that is movable from a first damperorientation that prevents nozzle spray from reaching the moving web anda second damper orientation in which spray reaches moving web, and themethod includes an idle/ready phase.
 28. The method of claim 1, claim 2,or claim 3 in which multiple nozzles are positioned on supports in ashower housing which includes a drain for excess adhesive.
 29. Themethod of claim 1, claim 2, or claim 3 in which includes providingmultiple nozzles at the first location, the nozzles being positioned onsupports in a shower housing which can be raised from a first inactiveposition to a second active position, the method including a period ofweb movement and bonding, followed by a period in which the web isslowed or stopped and the housing is moved from the active to theinactive position.
 30. The method of claim 1, claim 2 or claim 3 furthercomprising a nozzle purge cycle in which adhesive flow to the shower isstopped and flush water is introduced into the nozzles.
 31. The methodof claim 30 further comprising introducing purging airflow substantiallywithout liquid into the nozzles.
 32. The method of claim 1, claim 2 orclaim 3 in which at least 13% of the mixture sprayed is adhesive solids.33. The method of claim 1, claim 2 or claim 3 in which the webs move ata speed of at least 1500 feet/min during a significant portion of thebonding process.
 34. The method of claim 1 or claim 2 in which a firstof the reels of tissue is positioned on a rear tissue reel stand andunwound onto a path that includes in sequence a) a rear carrier roll, b)a forward carrier roll, and the nip, and a second of the tissue reels ispositioned on a forward reel stand and unwound onto the forward carrierroll underneath the first tissue web and then to the nip, and the spraylocation is adjacent to and downstream of, the rear carrier roll.